Sheathed welding wire

ABSTRACT

Provided is a welding wire and method for manufacturing a welding wire providing for quality welds on 300 series stainless steel and similar materials. A metal powder core is encapsulated in a metal sheath. The metal sheath composition comprising up to about 6% nickel, by weight, and may correspond to a series 400 stainless steel. A combination of the metal sheath and the metal powder core provides an overall alloy content of a series 300 stainless steel.

BACKGROUND

The invention relates generally to the field of welding systems and moreparticularly to sheathed welding wires that improve welding performance.

Welding systems generally make use of electrodes configured to pass anarc between a torch and a work piece, thereby heating the work piece tocreate a weld, and in certain welding systems melting the electrode toadd metal to the weld. A number of forms of welding are known and aregenerally used in the art. In many systems, such as metal inert gas(MIG) systems, the wire electrode is advanced through a welding torchand is generally consumed by the heat of the arc. In such operations,the wire electrode may also be known as a “filler material” that becomespart of the weld. The electrode may be provided in a variety ofmaterials and forms, including solid wire electrodes and metal-core wireelectrodes. Metal-core wire electrodes generally include tubular shapedmetal sheath about their exterior and a metal powder core includingvarious powdered materials.

The selection of the type of electrode for a particular weldingoperation may be based on several factors, including, the composition ofthe metals being welded, the joint design and the material surfaceconditions. In general, it is desirable that the weld electrode havemechanical properties similar to those of the base material and nodiscontinuities, such as porosity. Thus, desirable electrodes mayinclude solid wire electrodes or metal-core wire electrodes thatcomprise similar compositions to a work piece when they are melted intothe weld location. In other words, in a metal-core wire, the core of thewire and the sheath material surrounding the core may combine to definean overall composition when the wire is melted.

Further, the electrode may include properties that affect the quality ofthe weld. For example, an electrode may dictate the width of the arc,the heat of the weld, the depth of the weld, and the like. The electrodemay also affect the ease of welding. For example, a given electrode maybe susceptible to sticking of electrode to the work piece during weldingand, thus, increase the difficulty of welding.

In addition, depending upon the particular metallurgy of the weldingwire, aspects of the welding operation may be less than optimal. Forexample, certain applications may require specific wire metallurgy. Oneexample is in the manufacture of vehicle exhaust systems, in which solidseries 300 stainless steel welding wire is commonly used. However, dueto energy density issues, diameter and wetting/viscosity, incidences ofburn through can be high. Also, 300 series wire has a tendency tomicro-arc or stick during current transfer from the welding torchcontact tip to the wire. Such micro-arcing causes contact tip wear andfailure, as well as burn back. Moreover, the wire may freezemomentarily, creating process stability problems.

Accordingly, there is need for a welding wire that is compatible withwelding applications and that comprises properties that provide for aquality weld.

BRIEF DESCRIPTION

The invention provides a welding wire electrode designed to respond tosuch needs. In accordance with one aspect of the present invention, awelding wire comprises a metal core and a metal sheath encapsulating thecore. The metal sheath comprises a ferritic steel. The combination ofthe metal sheath and the metal core comprises an overall alloy contentof a 300 series stainless steel.

In accordance with another aspect of the present invention, a weldingwire comprises a metal core and a metal sheath encapsulating the core.The metal sheath comprises between about 16 and about 18% of chromium byweight and up to about 0.75% of nickel by weight. An alloyed combinationof the metal sheath composition and the metal core comprise comprisesbetween about 23 and 25% of chromium by weight and between about 12 and14% of nickel by weight.

A welding wire is also provided that has a series 400 stainless steelsheath, and a core that, in combination with the sheath, provides thewire with an overall composition of a series 300 stainless steel.

The present invention also provides a method of manufacturing a weldingwire. A metal sheath comprising up to about 6% of nickel by weight isfirst cupped, and a metal core material is disposed on the metal sheath.The combination of the metal sheath and the core provides an overallalloy content of a 300 series stainless steel. The metal sheath is thenclosed about the metal core material to form a wire, which may then bereduced a diameter of the wire and baked.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an exemplary welding system in which the wireelectrode of the present invention may be employed;

FIG. 2 illustrates an exemplary welding wire electrode of the system inFIG. 1 in accordance with aspects of the present technique;

FIG. 3 illustrates a cross section taken across line 3-3 of theexemplary welding wire of FIG. 2 in accordance one aspects of thepresent technique; and

FIG. 4 is a flowchart illustrating a method to manufacture the weldingwire of FIGS. 2 and 3 in accordance with one aspect of the presenttechnique.

DETAILED DESCRIPTION

Referring now to FIG. 1, welding system 10 is illustrated that employselectrode 12 in accordance with one embodiment of the present technique.As discussed in greater detail below, the electrode 12 includes ametal-core welding wire that is comprised of an outer sheath materialand a core material. For example, as described in greater detail below,the welding wire may include a metal sheath that encapsulates a metalcore material. As will be discussed in greater detail below, in oneembodiment, the metal sheath may comprise a ferritic steel and the metalcore material may comprise alloying elements such that the combinationof the metal sheath and the metal core material create a series 300series stainless steel. In other words, when the electrode 12 is melted,the compositions of the metal sheath and the metal powder core combineto form a series 300 series stainless steel filler material that isdeposited into the weld. As will be discussed below, embodiments of theelectrode 12 may create better arc-stability, better contact tip lifedue to reduced micro-arcing, reduced burn-through and produce smootherwelds.

As depicted, the MIG welding system 10 includes a power source 18, ashielding gas source 20, a wire feeder 22, electrode source 24 and awelding gun 26. In the illustrated embodiment, the power source 18 maysupply power to the electrode 12 via a power conduit 28 and the weldinggun 26. For example, a current may be provided to the electrode 12within the welding gun 26. In such a welding system 10, an operator maycontrol the location and operation of the electrode 12 by positioningthe electrode 12 and triggering the starting and stopping of the currentflow. In gas metal arc welding, the power source 18 typically willsupply a constant voltage that helps to maintain a stable arc length asthe distance from the electrode 12 to a work piece 30 is changed.

During a welding operation, wire feeder 22 advances wire electrode 12from the electrode source 24. For example, as depicted, the electrodesource 24 may include a spool that unwinds as the wire feeder 22 drawsthe wire electrode 12 and feeds it through the electrode conduit 32 andthrough the contact tip 34 of the welding gun 26. On the path to thecontact tip 34, the electrode 12 may be protected by a liner that helpsto prevent bucking and maintains an uninterrupted feed of wire. Theelectrode may be advanced through the gun when operator pulls a triggeron the welding gun 26 or provides another signal to advance theelectrode.

The welding arc is created as current flows from the tip of theelectrode 12 to the work piece 30 and returns to the power source 18.Therefore, the work piece 30 is generally grounded to the power source18 to provide a return path. For example, as depicted, a work clamp 36and cable 38 complete the electrical path between the work piece 30 andthe power source 18.

Some forms of arc welding may include a shielding gas to protect theweld area from atmospheric gases such as nitrogen and oxygen. Leftunprotected, these gases can cause fusion defects, porosity and weldmetal embrittlement. As depicted in FIG. 1, the shielding gas may beprovided to the gun 26 from a shielding gas source 20 via the gas supplyconduit 40. In some applications, the gas is automatically suppliedduring the welding operation and automatically shut-off when theoperation is interrupted. The flow of gas may be triggered by the sameswitch that initiates the feed of the wire electrode.

Further, the system 10 may include a control circuit 42 that coordinatesfunctions of the system 10. For example, the control circuit 42 may bein communication with the power source 18, the wire feeder 22 and/or theshielding gas source 20 to coordinate the operation of components of thesystem 10. Thus, the current, wire speed and gas may all stop and startin conjunction during welding.

As mentioned previously, during welding the arc created between theelectrode 12 and the work piece 30 melts the electrode 12 to provide afiller material to the weld location. In a typical application, theelectrode 12 is continuously fed to the weld location and consumedduring the welding process. Thus, the electrode 12 becomes part of thematerial used to create the weld, and the electrode materials maystrongly influence the mechanical properties of the weld. Accordingly,it is generally desired that the composition of the electrode 12 becompatible with the composition of the work piece 30. For example,manufacturers of exhaust systems may use a solid wire made of series 309stainless steel material on series 304 stainless steel manifolds,mufflers, and so forth.

Further, the electrode 12 may affect the ease of welding. For example,some electrodes may have a tendency to stick to the work piece 30 and,thus, create vibration during welding, or even interrupt the steady flowof wire to the torch. It has been found that 300 series stainless steelwires pose particular difficulties in welding, believed due to thepresence of specific alloying materials in specific percent ranges atthe surface of the wire. That is, the very composition of the 300 seriesstainless steel, desirable in the weld, renders the welding wiredifficult to use. To accommodate such applications, the presenttechnique provides an electrode wire specifically designed to offer acomposite metallurgy but in a jacket or sheath that prevents or reducesthe adverse effects of the 300 series stainless steel composition at thesurface of the electrode wire.

As illustrated in FIGS. 2 and 3, in an embodiment of the presenttechnique, an electrode 12 that has an overall composition of a series300 stainless steel may include a ferritic steel metal sheath 14. Thecore of the electrode wire includes alloying materials that result, incombination with the ferritic steel sheath 14, in the overallcomposition meeting series 300 stainless steel specifications. Throughuse of the composite wire of the invention, an electrode 12 including aferritic steel sheath has been shown to reduce or eliminate micro-arcingdue to the absence or reduction of nickel in the ferritic steel metalsheath 14. In addition, the ferritic stainless steel metal sheath 14 mayimprove wetting of the weld location and, thus, reduces the angle of theweld pool bead to the work piece 30. The reduced angle is believed toreduce burn through and create better gap filling. Further, the BCCcrystal structure of ferritic steels may provide desirable electricalproperties.

Ferritic stainless steels are highly corrosion resistant. They containbetween 10.5% and 27% chromium and very little nickel. Most compositionsinclude molybdenum, aluminum or titanium. A ferritic stainless steel mayinclude type 400 series stainless steels. Accordingly, the compositionof the metal sheath 14 may include various 400 series stainless steelsconfigured to accommodate numerous applications. In one embodiment, themetal sheath 14 may comprise a nickel content that is below about 6% byweight. For example, the metal sheath 14 may comprise a series 430stainless steel (UNS S43000) that comprises between about 16 and 18%chromium, up to about 0.12% carbon, up to about 1% manganese, up toabout 1% silicon, up to about 0.04% phosphorus, up to about 0.03%sulfur, and up to about 0.75% nickel, all percentages being by weight.

The metal sheath 14 may also be formed from other series 400 stainlesssteel metals. For example, the metal sheath may be formed from series409, or series 439 stainless steel. The series 409 stainless steel (UNSS40900) may comprise between about 10.5% and 11.75% chromium, up toabout 0.08% carbon, up to about 1% manganese, up to about 1% silicon, upto about 0.045% phosphorus, up to about 0.03% sulfur, and up to about0.5% nickel, all percentages again being by weight. The series 439stainless steel (UNS S43035) may comprise between about 17% and 19%chromium, up to about 0.07% carbon, and up to about 0.5% nickel, forexample.

The present technique relies upon combining a series 400 stainless steelsheath 14 with a powder core 16 to provide an overall composition of aseries 300 stainless steel. For example, the metal powder core 16 maycomprise a core composition, as well as number of alloying elements toproduce an electrode with an overall composition of a 300 seriesstainless steel when the electrode 12 is melted. Generally, the materialof the metal powder core 16 may comprise iron. Additional alloyingelements may include chromium, nickel, carbon, molybdenum, manganese,silicon, phosphorous, sulfur, copper and the like. The relative amountsof iron and alloying elements may be varied, along with the compositionof the sheath 14 to provide an overall composition of the welding wireelectrode 12. For example, as more of one element is added to the metalsheath 14, the amount of the elements in the metal powder core 16 may bereduced. The metal powder core 16 is not limited to materials in powderform, but may include any form of material that provides the desiredoverall composition.

As a general characteristic, a series 300 overall composition mayinclude between about 6% and 40% nickel and between about 10% and about35% chromium. In one embodiment, the overall composition may meet thespecifications of a series 309 stainless steel. The series 309 stainlesssteel (UNS S30980) may comprise between about 23% and 25% chromium, upto about 0.12% carbon, up to about 0.75% molybdenum, between about 1%and 2.5% manganese, between about 0.3% and 0.65% silicon, up to about0.03% phosphorus, about 0.03% sulfur, up to 0.75% copper, and betweenabout 12% and 14% nickel, all by weight.

In other embodiments, the overall composition of the electrode 12 mayinclude other series 300 stainless steels. For example, embodiments mayinclude overall compositions of series 309LSi, 308, 316 or 317 stainlesssteels. The series 309LSi stainless steel (UNS S30988) may comprisebetween about 23% and about 25% chromium, up to about 0.03% carbon, upto about 0.75% molybdenum, between about 1% and 2.5% manganese, betweenabout 0.65% and 1% silicon, up to about 0.03% phosphorus, about 0.03%sulfur, up to 0.75% copper, and between about 12% and 14% nickel, all byweight.

In an embodiment of a series 308 stainless steel (UNS S30800) theoverall composition may comprise between about 19% and about 21%chromium, up to about 0.08% carbon, up to about 2% manganese, up toabout 1% silicon, up to about 0.045% phosphorus, about 0.03% sulfur, andbetween about 10% and 12% nickel, all by weight.

In an embodiment of a series 316 stainless steel (UNS S31600) theoverall composition may comprise between about 16% and about 18%chromium, up to about 0.08% carbon, between about 2% and 3% molybdenum,up to about 2% manganese, up to about 0.75% silicon, up to about 0.045%phosphorus, about 0.03% sulfur, up to about 0.1% nitrogen, and betweenabout 10% and 14% nickel, all by weight.

In an embodiment of a series 317 stainless steel (UNS S31700) theoverall composition may comprise between about 18% and about 20%chromium (Cr), up to about 0.08% carbon, between about 3% and 4%molybdenum, up to about 2% manganese, up to about 0.75% silicon, up toabout 0.045% phosphorus, about 0.03% sulfur, up to about 0.1% nitrogen,and between about 11% and 15% nickel, all by weight.

Further, various methods may be employed to manufacture a metal corewire electrode 12 comprising a ferritic steel sheath 14 and an overallcomposition of a series 300 stainless steel. For example, a method formanufacturing a metal core wire is depicted in FIG. 4. A step inproducing the metal-core wire electrode 12 may include cupping a metalsheath strip as shown at block 42. In one embodiment, a continuous stripof metal sheath material may be provided and manipulated to form acup-shaped trough. For example, an embodiment may include providing agenerally continuous flat strip of series 400 metal and rolling theedges of the strip to form a trough shaped strip of metal sheathmaterial.

Next, the method may include a step of depositing the metal powder coreas depicted at block 44. An embodiment may include a device depositing acomposition of the metal powder core 16 into the trough of thecupped-shaped strip of the metal sheath material. For example, as agenerally continuous length of the cupped metal sheath 12 passes adeposition station, a mechanism may deposit a continuous stream of themetal powder core 16, including iron and other alloying elements, intothe progressively cupped trough. Thus, the metal core composition willrest within the trough of the metal sheath material as the sheath isprogressively closed around it.

With a bead of metal powder core 16 deposited along the length of thecupped metal sheath 12, the metal sheath 12 may be closed to encapsulatethe metal powder core 16, as summarized at block 46. In one embodiment,the length of metal sheath 12 with the deposited metal powder core 16may be advanced through one or more progressive rolling stations thatroll the cupped metal sheath 14 into a tubular enclosure about the metalpowder core 16. As the metal sheath 12 is rolled about the powder core,the pressure of the rolling may form a seam along the length of thesheath 14. Thus, a substantially round wire is formed including themetal sheath 14 about the powder metal core 16.

Subsequent to closing the metal sheath about the metal powder core(block 46), the diameter of the wire electrode 12 may be manipulated(e.g., reduced) to a desired dimensions, as depicted at block 48. In oneembodiment, the closed metal sheath 14 and core 16 may be advancedthrough an additional rolling station configured to reduce the diameterto provide an appropriate round wire shape. A moderate size wire mayinclude about 0.0625 inches in outer diameter, and a small wire mayinclude a diameter of about 0.035 to 0.045 inches. In one embodiment, alarger wire may comprise a diameter of about 0.0983 inches. It is alsoworth noting that the rolling technique may also complete the seamformed at the edges of the metal sheath 14.

Finally, the wire may be baked, as depicted at block 50. Baking the wiremay remove moisture from the wire and consolidate the core materials.For example, the reduced diameter wire may be baked at 600° F.-700° F.to promote the removal of moisture through the seam of the metal sheath14. In one embodiment, the wire electrode 12 may be continuouslyadvanced through an oven during the manufacture process to provide evenheating across the wire electrode 12.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1-25. (canceled)
 26. A welding wire, comprising: a metal sheathcomprising a 430 stainless steel; and a core encapsulated by the sheath,an alloyed combination of the metal sheath and the core comprising a 309stainless steel.
 27. The welding wire of claim 26, wherein the sheathcomprises between about 16 and 18% chromium and up to about 0.75%nickel, all by weight.
 28. The welding wire of claim 26, wherein thealloyed combination of the metal sheath and the core comprises betweenabout 23 and 25% chromium and between about 12 and 14% nickel, all byweight.
 29. The welding wire of claim 26, wherein the alloyedcombination comprises less than about 0.12% carbon.
 30. The welding wireof claim 26, wherein the alloyed combination comprises between about0.65 and 1% silicon, by weight.
 31. The welding wire of claim 26,comprising an outer diameter equal to or less than approximately 0.0625inches.
 32. The welding wire of claim 26, comprising an outer diameterof between approximately 0.035 inches and 0.045 inches.
 33. A weldingwire, comprising: a metal sheath comprising a 439 stainless steel; and acore encapsulated by the sheath, an alloyed combination of the metalsheath and the core comprising a 309 stainless steel.
 34. The weldingwire of claim 33, wherein the sheath comprises between about 17 and 19%chromium and up to about 0.5% nickel, all by weight.
 35. The weldingwire of claim 33, wherein the alloyed combination of the metal sheathand the core comprises between about 23 and 25% chromium and betweenabout 12 and 14% nickel, all by weight.
 36. The welding wire of claim33, wherein the alloyed combination comprises less than about 0.12%carbon.
 37. The welding wire of claim 33, wherein the alloyedcombination comprises between about 0.65 and 1% silicon, by weight. 38.The welding wire of claim 33, comprising an outer diameter equal to orless than approximately 0.0625 inches.
 39. A method of manufacturing awelding wire, comprising: cupping a metal sheath strip comprising a 430or 439 stainless steel; disposing a metal core material on the metalsheath, a combination of the metal sheath and the metal core materialcomprising an overall alloy content of series 309 stainless steel;closing the metal sheath about the metal core material to form a wire;reducing a diameter of the wire; and baking the wire.
 40. The method ofclaim 39, wherein the sheath comprises between about 16 and 18% chromiumand up to about 0.75% nickel, all by weight.
 41. The method of claim 40,wherein the alloyed combination of the metal sheath and the corecomprises between about 23 and 25% chromium and between about 12 and 14%nickel, all by weight.
 42. The method of claim 39, wherein the sheathcomprises between about 17 and 19% chromium and up to about 0.5% nickel,all by weight.
 43. The method of claim 42, wherein the alloyedcombination of the metal sheath and the core comprises between about 23and 25% chromium and between about 12 and 14% nickel, all by weight. 44.The method of claim 39, wherein the alloyed combination comprises lessthan about 0.12% carbon.
 45. The method of claim 39, wherein baking thewire comprises baking at a temperature between about 600° F. and 700° F.